As of now, the oldest structure on G-Urth, being around 7,500,000,000 years old (as revealed by the Slam Energy surrounding its composition). It is a small domed building shaped to look like the screaming face of Pumpatron. There is no way to actually "enter" the building, because the mouth-entrance is a chute leading directly to a part of Hell that is a 1000:1 scale model of the Slam God digestive system. This fact makes Howl Head the oldest practical joke in history, too.
Pumpatron has gone on record saying that he is unimpressed with the artist's rendering of his face, and does not appreciate being connected to Hell, however circuitously, but has agreed to let cultural authorities preserve the site. Currently, Howl Head has fifteen penises graffitied on its exterior.